JPH10233305A - Voltage nonlinear resistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a voltage nonlinear resistor comprising ZnO as a main component which is highly reliable without causing any thermal runaway. SOLUTION: ZnO is provided as a main component, to which accessory components are added including, all by atomic ratio of metallic element, 0.08-5.0at%, in total, of at least one rare-earth element, 0.1-10.0at% of cobalt, 0.1-0.5at% of calcium, 0.01-1.0at%, in total, of at least one of potassium, cesium and rubidium, 0.1-0.6at% of chromium, 1×10<-4> -5×10<-2> at.%, in total, of at least one of aluminum, gallium and indium, 0.5-2.0at% of antimony, and 0.2-1.5at% of bismuth, followed by sintering to provide a resistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a voltage non-linear resistor,
For details, use zinc oxide (Z
nO) as a main component.

[0002]

2. Description of the Related Art A voltage non-linear resistor mainly composed of ZnO has characteristics such as a low limit voltage and a large voltage non-linear index. Therefore, it is widely used as an arrester element for the purpose of protection against overvoltage of a device constituted by a device having a small overcurrent capability such as a semiconductor device or protection of a power device.

In this connection, for example, zinc oxide (ZnO) is used as a main component, and at least one rare earth element in a total amount of 0.08 to 5.0 as an auxiliary component in an atomic ratio of a metal element.
Atomic%, cobalt (Co) 0.1 to 10.0 atomic%, magnesium (Mg), at least one of calcium (Ca)
5.0 atomic%, potassium (K), cesium (Cs), rubidium
At least one of (Rb) in a total amount of 0.01 to 1.0 atomic%,
Chromium (Cr) 0.01 to 1.0 atomic%, boron (B) 5 × 10 ^-4
~ 1 × 10 ^-1 atomic%, aluminum (Al), gallium (Ga),
At least one of indium (In) is 1 × 10 ^{-4 in} total amount
It is found that an excellent voltage non-linear resistor can be manufactured by adding and firing in the range of 5 × 10 ^-2 atomic%.
No. 5205.

[0004]

However, as described above, a voltage non-linear resistor (hereinafter, referred to as a zinc oxide (ZnO)) as a main component (hereinafter referred to as a zinc oxide (ZnO)).
ZnO resistors) also have the following problems. The ZnO resistor is used by being directly connected to a power supply line or the like without adding a series gap or the like due to its excellent nonlinearity. In such a conventional resistor, the leakage current flowing in an applied state at all times is very small, but the leakage current gradually increases due to deterioration due to long-time application of power or deterioration due to surge absorption, and heat is generated by the increased current. Eventually, the balance of emission and heat radiation may be disrupted, causing thermal runaway.

In order to suppress such thermal runaway of the ZnO resistor, it is conceivable to use it while suppressing the power application rate (the ratio of the actual applied voltage to the terminal voltage of the ZnO resistor when a current of 1 mA is applied). In addition, it is conceivable to increase the allowable power. Here, the permissible power is a measure of the life of the ZnO resistor, and the minimum constant voltage is selected from the constant voltages whose current increases within 10 minutes after application. It is defined by the product of the initial current when a constant voltage is applied. This allowable power is used as a simple alternative to life testing. A ZnO resistor with a large allowable power is
High reliability without heat runaway.

As a method of reducing the leakage current of the ZnO resistor or increasing the allowable power, a method of sintering the ZnO resistor in an oxygen atmosphere or a method of reducing the amount of Al added to the ZnO resistor is used. A method of heat-treating the sintered body was considered. However, the method of firing such a ZnO resistor in an oxygen atmosphere or reducing the amount of Al added to the resistor has a disadvantage that the limiting voltage in a large current region is increased, and The method of heat-treating the sintered body has a problem that extra cost is required for the heat treatment.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to reduce the electric characteristics such as voltage non-linearity without performing heat treatment and to reduce the voltage non-linear resistance of a conventional voltage non-linear resistor. It is an object of the present invention to provide a voltage non-linear resistor having a remarkably large allowable power, that is, a life characteristic greatly improved.

[0008]

In order to solve the above-mentioned problems, a ZnO resistor having ZnO as a main component and various sub-components added thereto is prototyped, and allowable power is evaluated to determine an optimum composition range. did. That is, the voltage non-linear resistor of the present invention is ZnO
As a main component, and at least one rare earth element in a total amount of 0.08 to 5.
0 atomic%, 0.1 to 10.0 atomic% of Co, 0.1 to 1.0 atomic% of Ca, 0.01 to 1.0 atomic% of at least one of K, Cs and Rb, 0.1 to 1.0 atomic% of Cr, Al, Ga, In At least one of them has a total composition of 1 × 10 ^{−4 to} 5 × 10 ^{−2 at} %, and further contains 0.5 to 2.0 at% of Sb and 0.2 to 1.0 at% of Bi.
It shall be added and fired in the range of 5 atomic%.

As another means, it is assumed that B is added in the range of 5 × 10 ^-4 to 1 × 10 ^-1 atomic% in addition to the above as an auxiliary component, followed by firing. The composition range of the non-linear resistor according to the present invention limits the amount of Ca added in the components of the voltage non-linear resistor disclosed in Japanese Patent Publication No. 1-25205,
It was like adding Sb and Bi.

The mechanism by which the allowable power is increased by adding Sb and Bi has not been elucidated. However, since the allowable power reflects the life characteristics of the ZnO resistor, it can be considered that the addition of a certain amount of Sb or Bi improves the life characteristics, that is, suppresses the deterioration. It is believed that the degradation of the ZnO resistor is due to migration of interstitial Zn ions near the grain boundaries. Therefore, it is considered that the ions of Sb and Bi enter between the ZnO lattices near the crystal grain boundaries and hinder the movement of the Zn ions by the electric field, and as a result, deterioration is suppressed.

[0011] This effect is also achieved by adding ZnO with a small amount of boron.
The same holds true for resistors. Further, when boron having a large particle size is added, boron is an element having a high vapor pressure, so that the concentration in the peripheral portion is reduced, and the particle size in the peripheral portion is smaller than that in the central portion. Therefore, the current sharing in the peripheral portion, where the current tends to concentrate in the past, is reduced. Note that Sb,
A voltage non-linear resistor containing Bi is described, for example, in Japanese Patent Publication No. 57-49124.
And JP-B-63-29803 and JP-B-2-49525, all of which contain oxides of Mn and Si as necessary components.

On the other hand, the voltage nonlinear resistor of the present invention does not contain oxides of Mn and Si as necessary components. Especially
If Si is mixed in, the resistance in the low current region decreases, and stable voltage non-linearity cannot be obtained. Therefore, it is excluded from the components and is different from the above-mentioned known example.

[0013]

Embodiments of the present invention will be described below. The voltage non-linear resistor according to the present invention is manufactured by firing a mixture of ZnO and a metal or a compound as an additional component at a high temperature in an oxygen-containing atmosphere and sintering the mixture. The additional component is added in the form of a metal oxide, but a compound that can be converted into an oxide in the firing step, for example, a carbonate, a hydroxide, a boride and a solution thereof, or the like can be used, or in the form of a single element. It can be used and converted into an oxide during the firing process.

Next, a specific example of the voltage non-linear resistor according to the present invention will be described. [Example 1] Table 1 shows the measurement results of the composition and electrical characteristics of the voltage nonlinear resistor.

[0015]

[Table 1]

Praseodymium oxide (Pr ₆ O ₁₁ ), ZnO powder,
Cobalt oxide (Co ₃ O ₄ ), calcium carbonate (CaCO ₃ ), potassium carbonate (K ₂ CO ₃ ), chromium oxide (Cr ₂ O ₃ ), aluminum oxide (Al ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃₎ ), Antimony oxide
(Sb ₂ O ₃ ) powder was added in an amount corresponding to the specified atomic% shown in Table 1, and after adding a binder and mixing well,
It was pressed into a disk having a diameter of 17 mm and fired in air at 1100 to 1400 ° C for 1 hour to obtain a sintered body. The composition shown in Table 1 is the atomic% calculated from the ratio of the number of atoms of the additive element to the total number of atoms of each component metal element in the blended raw material.
It is represented by

The obtained sintered body was polished into a sample having a thickness of 1 mm, and the electrical characteristics of the resistor were measured. The electrical characteristics are V1m, which is the voltage between terminals when a current of 1 mA flows through the resistor.
A and allowable power were determined. The allowable power was measured at a temperature of 105 ° C. in a thermostatic chamber in consideration of a case where a surge was absorbed in a use state or a case where a leakage current was increased due to deterioration due to voltage application and a temperature was raised.

Each of the samples in Table 1 was prepared by adjusting the firing temperature so that the varistor voltage (ie, V1mA per unit thickness = V1m) was obtained.
A / t) is set to 180 to 220V / mm. Sample No. 1 in Table 1
Is manufactured by adding praseodymium (Pr), Co, Ca, K, Cr and Al to ZnO (that is, without adding Bi and Sb). Table 1 also shows the measurement results of the allowable power of each sample as an allowable power ratio, which is a magnification with respect to the allowable power of this sample. Therefore, the larger the value of this ratio, the better.

First, the effects of Sb addition can be read from Sample Nos. 2 to 7. In other words, sample N has the larger allowable power ratio.
o.3 to 6, an appropriate Sb component ratio is 0.5
It can be seen that it is about 2.0 atomic%. From the samples Nos. 8 to 12 and No. 4, the effect of the addition of Bi can be read. That is, since the sample Nos. 4 and 9 to 11 have the large allowable power ratios, it can be seen that the appropriate Bi component ratio is 0.2 to 1.5 atomic%. Sample N to which Sb and Bi were added
In o.2 to 12, the leakage current after the long-term application test was
The effect was also reduced by about 20 to 30% compared to.

The following samples Nos. 13 to 42 were prepared by fixing Pr, Co, Ca, K, Cr and Al added as sub-components to the basic composition ZnO resistor after fixing Sb and Bi in an appropriate amount. This is the result of examining an appropriate range. For example, sample N in which the amount of added Pr was changed
In o.38 to 42, since the allowable power ratio of sample Nos. 39 to 41 is larger than 1, an appropriate Pr component ratio is 0.08 to 5.0
It can be seen that the content is atomic%. Sample N with different amount of Co added
The appropriate Co component ratio from o.33 to 37 is 0.1 to 10.0 atomic%, and the appropriate Ca
From the sample Nos. 23 to 27 in which the addition ratio of K was varied from 0.1 to 1.0 atomic% as the component ratio, the appropriate K component ratio was 0.01 to 1.0 atomic%.
The appropriate Cr component ratio from Sample Nos. 18 to 22 with 1.0 atomic% and the added amount of Cr is 0.01 to 1.0 atomic%, and the appropriate Al component from Sample Nos. 13 to 17 with the added amount of Al changed. As a ratio,
It can be seen that the content is 0.0001 to 0.05 atomic%.

That is, Pr, Co, Ca, K, Cr, Al, Sb,
By limiting the amount of Bi added to the above range, a ZnO resistor having a large allowable power was obtained. Example 2 Table 2 shows the results of measurement of the composition and electrical characteristics of the voltage non-linear resistor.

[0022]

[Table 2]

[0023] ZnO _{powder, Pr 6 O 11, Co 3} O 4, CaCO 3, K 2
CO ₃ , Cr ₂ O ₃ , boron oxide (B ₂ O ₃ ), Al ₂ O ₃ , antimony oxide (Sb ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ) %, And the mixture was sufficiently mixed with a binder. The mixture was pressed into a disk having a diameter of 17 mm and fired in air at 1100 to 1400 ° C. for 1 hour to obtain a sintered body. It is known that the addition of a small amount of boron changes the grain size distribution of the ZnO resistor after firing, reduces the peripheral grain size, smoothes the stress distribution, and increases the surge resistance of the ZnO resistor.

Table 2 also shows the measurement results of the allowable power. Table 2
Sample No. 101 was prepared by adding Pr, Co, Ca, K, Cr, B, and Al to ZnO (ie, without adding Sb and Bi). In the table, the allowable power ratio, which is a magnification with respect to the allowable power of the sample, is shown. Therefore, the larger the value of this ratio, the better. The varistor voltage (V1mA per unit thickness = V1mA = V
1mA / t) is set to 180 to 220V / mm.

First, the effects of Sb addition can be read from Sample Nos. 102 to 107. That is, since the sample Nos. 103 to 106 have a large allowable power surface layer, it is understood that the appropriate Sb component ratio is 0.5 to 2.0 atomic%. Sample N
From o.104 and the following Nos. 108 to 112, the effect of adding Bi can be read. That is, the allowable power surface layer is large for sample 10
4 and Nos. 109 to 111, it is understood that a suitable Bi component ratio is 0.2 to 1.5 atomic%.

From the combined data of the following samples Nos. 113 to 148 and the above No. 104, it was found that Pr, Co, Ca, K, Cr, B, and B added as auxiliary components to the ZnO resistor having the basic composition. The effect of Al can be read. For example, sample No. 1 in which the amount of added Pr was changed
In the case of 44 to 148, since the allowable power ratio of sample Nos. 145 to 147 is larger than 1, the appropriate Pr component ratio is 0.08 to 5.0
It can be seen that the content is atomic%. Similarly, from the sample Nos. 139 to 143 in which the amount of Co added was changed, as the appropriate Co component ratio,
Sample Nos. 134 to 13 with 0.1 to 10.0 atomic% and different amounts of Ca added
From 8 it is found that the appropriate Ca component ratio is 0.1-1.0 atomic%, K
From the sample Nos. 129 to 133 in which the addition amount of Cr was changed, the appropriate K component ratio was 0.01 to 1.0 at%, and the sample in which the addition amount of Cr was changed.
From No.124-128, a suitable Cr component ratio is 0.01-1.0
The appropriate B component ratio from the sample Nos. 113 to 118 in which the atomic% and the B addition amount were changed was 0.0005 to 0.1 atomic%, and the appropriate Al component ratio from the sample Nos. Is from 0.0001 to 0.05 atomic%.

That is, in this example in which boron is added,
By limiting the amount of addition of a, Cr, Al, Sb, etc. to the above range, Zn having a large allowable power and a large surge withstand capacity.
An O resistor was obtained. In the above examples, only Pr was shown as a rare earth element to be added as an auxiliary component, but rare earth elements other than Pr, for example, lanthanum (La), neodymium (Nd),
Samarium (Sm), Terbium (Tb), Dysprosium (Dy)
Or a plurality of these elements may be used. In addition, K may be Cs and Rb, or K, Cs, and Rb may be simultaneously added, and Al may be simultaneously added of Ga, In, or Al, Ga, and In. It has been separately confirmed by experiments that the same effects as described above, which is the main feature of the present invention, can be obtained even in a composition system to which these subcomponents are added.

[0028]

As described above, ZnO is the main component,
In addition to the basic composition to which other auxiliary components such as rare earth elements are added,
Furthermore, the voltage non-linear resistor of the present invention fired by adding Bi and Sb does not require sintering in an oxygen atmosphere, heat treatment, etc., and has a higher allowable power than before without reducing various electric characteristics such as voltage non-linearity. The characteristics can be increased and an element having excellent reliability can be obtained.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kazuo Mukai 1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd.

Claims (2)

[Claims] (1) Zinc oxide as a main component, and as an auxiliary component, at least one rare earth element in a total amount of 0.08 to 5.0 at.% And cobalt in a 0.1 to 1 at.
0.0 at%, calcium at 0.1-1.0 at%, potassium, cesium, at least one of rubidium in total amount of 0.01-1.0 at%, chromium of 0.01-1.0 at%, at least one of aluminum, gallium, indium at total amount 1 × 10 ^{-4 to} 5 × 10 ^-2 atomic%, bismuth 0.2 to
A non-linear voltage resistor characterized in that 1.5 atomic% and antimony are added in the range of 0.5 to 2.0 atomic% and fired. 2. The method according to claim 1, wherein the sub-component is an atomic ratio of a metal element.
5 x 10^-Four~ 1 × 10 ^-1Add in the range of atomic% and bake
The voltage non-voltage according to claim 1 or 2,
Linear resistor.